Aerosolized black carbon absorption measurements with optical fiber based system

We propose here an efficient method to directly and linearly measure the aerosol absorption coefficient with an instrument featuring a small footprint and ease of operation. We will develop an instrument to measure aerosol light absorption for laboratory and field use. The instrument will serve as the reference for aerosol light absorption from which black carbon mass concentration can be precisely inferred. The instrument will be based on first principles, can be easily calibrated and will, be usable as a standard for existing black cabron and aerosol absorption instruments. It will combine everything for successful commercialization: robustness, simplicity, precision, and accuracy. The photothermal interferometer measures aerosol absorption linearly and traceably to first principles. Aerosol laden air is drawn through the sample chamber. A powerful modulated pump laser illuminates this sample and some of the light is absorbed by the aerosols. These heat up, transferring heat to the surrounding air. Air density reduces, reducing its refractive index. This change in the refractive index is measured as the optical path difference in an interferometer. The modulation of the phase change is linearly related to the absorption coefficient. We will realize the pumping and the interferometer in a fiber photo-thermal interferometer, substantially simplifying the experimental arrangement and making the measurement simpler, more robust and less prone to external influence (and therefore noise). In the scope of the project we will: 1. determine the optimal experimental arrangement, 2. research and develop the subcomponents taking advantage of this arrangement, 3. combine the subcomponents into the fiber photo-thermal interferometer, 4. validate the instrument in the laboratory, including calibration, and 5. verify its operation by measuring ambient aerosol absorption in challenging field conditions.